The present invention is directed to an optical coupling device and more specifically to an optical coupling device for coupling the light transmitting end of an optical fiber to the light sensitive area of a photo-semiconductor element with minimum loss of light.
A typical prior art optical coupling arrangement for transmitting light from the end of an optical fiber to the light sensitive area of a photo-semiconductor element is shown in FIG. 1. The photo-semiconductor element is comprised of a cathode 12, an N.sub.B layer 13, a P.sub.E layer 14, an N.sub.B layer 15, a P.sub.E layer 16, an anode 17 and a light receiving section 18 covered with a reflection preventing film 19. The reflection preventing film 19 is made from a polyimide or silicon oxide. An optical fiber 20 is arranged with the end face 20a disposed opposite the light sensitive area 18 in spaced relation thereto. The opposite end face of the optical fiber 20 which is not illustrated in FIG. 1 may be coupled to a photo-diode or any other suitable light source. Light from the photo-diode is transmitted through the optical fiber 20 and is emitted from the end face 20a. The light H emitted from the end face 20a reaches the light sensitive area 18 through the reflection preventing film 19 to trigger the photo-semiconductor element 10.
In the above-described prior art arrangement, the light H emitted from the end face 20a of the optical fiber 20 is in general spread angularly with respect to the central axis of the optical fiber. Therefore, a portion of the light H can spread laterally through the clearance between the end face 20a of the optical fiber and the upper surface 10a of the photo-semiconductor element thereby decreasing the quantity of light received by the light sensitive area 18.